For performing a U-turn guidance, as shown in FIG. 9, a conventional navigation system contains information on a U-turn guidance (U-turn guidance information) in both of the node record of a front node 311 of a link 301 corresponding to one lane of the road having a medial strip, and the node record of a front node 312 of a link 302 corresponding to the other lane. Accordingly, if at least one of the node records is not contained in the U-turn guidance information due to a data input error or the like, the conventional navigation system does not perform the U-turn guidance regardless of whether a U-turn is possible.
In another case where a wide medial strip exists, the driver may make a right turn or a left turn twice to turn around from a lane in one traveling direction on to a lane in the other traveling direction instead of making a U-turn. Even in this case, the conventional navigation system performs U-turn guidance in a manner confusing to the driver.
Some navigation systems prompt a driver to make a U-turn by showing a U-turn mark on the display in situations where the searched guidance route contains a road having a medial strip and where the driver must turn around from a lane in one direction to a lane in the other direction. (refer to Japanese Patent Application Publication No. 1998(H10)-227649, for example).